Technical Abstract:
Southeastern Oregon harbors extensive blocks of Wyoming big sagebrush steppe in mid to late seral ecological stages. These areas are co-dominated by sagebrush and perennial bunchgrasses with a limited presence of cheatgrass. However, cheatgrass has the potential to alter these systems after fire by conversion from native to annual dominated systems. This change is a major factor for the loss of habitat for sagebrush obligate and facultative wildlife species in the Great Basin. There is a lack of information on the effects of wildfire in the ARTRWY alliance in remaining intact areas. Information is needed to evaluate post-burn successional dynamics and to develop risk assessments of community susceptibility to cheatgrass or other weed invasion after fire. This study evaluated early succession for 5 years after wildfire on two Wyoming big sagebrush (ARTRWY) plant associations in southeast Oregon. Associations were ARTRWY/Thurbers needlegrass (STTH) and ARTRWY/bluebunch wheatgrass (AGSP). Recovery has differed among the two associations. The STTH association was severely impacted by the wildfire. Sandbergs bluegrass (Poa sandbergii Vasey), Thurbers needlegrass, and mat forming perennial forbs were significantly reduced and have not recovered. Cheatgrass increased 7 fold but has not dominated the STTH association. Herbaceous cover in the AGSP association recovered rapidly, returning or exceeding pre-burn levels by the 3rd or 4th year post-fire. Perennial and annual forb cover increased in the AGSP association although forb composition was altered. Cheatgrass remained a minor to nonexistent component in the AGSP association. The high mortality of perennial grasses and presence of cheatgrass in the Thurbers needlegrass association suggests there is a risk for annual grass replacement of this steppe association. Bluebunch wheatgrass and Thurbers needlegrass associations are often found in a mosaic on the landscape. Therefore efforts should probably be made to limit wildfire disturbance in ARTRWY plant associations in southeast Oregon.